Single wheel, self-balancing boards are known. Such vehicles permit a rider to stand thereon to travel across generally flat surfaces. FIG. 1 shows such a single wheel, self-balancing board 20. The single wheel, self-balancing board 20 has a platform 24 that includes a pair of foot deck surfaces 28 at its longitudinal ends that are bridged by a pair of lateral frame members 32 extending along the lateral sides of the platform 24. The foot deck surfaces 28 and the lateral frame members 32 define a wheel opening 36 between them. A wheel assembly 40 is positioned in the wheel opening 36 and secured to the lateral frame members 32 via an axle. A motor of the wheel assembly 40 is coupled to the axle and drives a tire 44 to rotate clockwise or counter-clockwise around the axle. A controller controls the motor to maintain the platform 24 generally level horizontally in response to data from sensors.
The tire 44 is pneumatic, providing an air cushion for dampening impact forces, and has a central circumferential surface 48 that has a uniform, generally smooth tread that is free of grooves. The generally smooth central circumferential surface 48 extends laterally to meet two beveled lateral circumferential portions 52 at the circumferential edges 56. The beveled lateral circumferential surfaces 52 extend to the sidewalls 60 of the tire 44.
FIG. 2A shows the tire 44 in contact with a generally flat travel surface 64 when a rider's weight is evenly distributed laterally across the platform 24 of the single wheel, self-balancing board 20. As a result of the laterally evenly distributed weight of the rider, deformation of the tire 44 is generally even across its lateral dimension, resulting in a contact patch 68 with the travel surface 64 that spans the lateral width of the central circumferential surface 48. Traction between the tire 44 and the travel surface 64 provides resistance to travel of the single wheel, self-balancing board 20 in a direction other than those orthogonal to the central circumferential surface 48 of the tire 44.
A rider standing on the platform 24 can cause the single wheel, self-balancing board 20 to change travel direction by shifting their weight to a lateral side of the platform 24, causing the corresponding lateral side of the tire 44 to be compressed.
FIG. 2B shows the tire 44 of the single wheel, self-balancing board 20 in contact with the generally flat travel surface 64 with a rider's weight shifted to a lateral side of the platform 24 of the single wheel, self-balancing board 20. The pneumatic tire 44 compresses and deforms on the lateral side to which weight has been shifted, leading to a reduction in size of a contact patch 68′ between a lateral portion of the central circumferential surface 48 and the travel surface 64. Further, the deformation causes a reduction in the effective profile of the pneumatic tire 44 so that it becomes effectively tapered towards its lateral sides (i.e., frustoconical), thus enabling travel in a direction that is not perpendicular to the rotation axis of the pneumatic tire 44. The sidewall 60 on the lateral side of the tire 44 to which weight has been shifted is deformed but has a natural tendency return to its original shape as shown in FIG. 2A due to a restoring force in the side wall of the tire 44. As a result, if the rider desires to experience a ‘carving’ motion as they would on a snowboard or surfboard, they must continually counter this restoring force F while leaning to one lateral side of the platform 24. As will be appreciated, the effort of the rider to maintain weight shifted to one lateral side of the platform 24 to counter the lateral centering force F can make smooth changes in direction of the single wheel, self-balancing board 20 difficult.
Further shifting weight to one lateral side of the platform 24 by the rider further reduces the size of the contact patch 68′ between the tire 44 and the travel surface 64 to a region of the central circumferential surface 48 of the tire 44 adjacent the circumferential edge 56 on the lateral side of the platform 24 to which weight has been shifted. As the contact patch 68′ between the tire 44 and the travel surface 64 is reduced, the rider can cause the single wheel, self-balancing board 20 to change directions more readily by continued shifting of their weight to the lateral side of the platform 24 or by relative shifting of one of their feet resting on the foot deck surfaces 28a, 28b to reorient the platform in a different direction. As will be understood, however, the centering force F increases as the weight shift increases.